Plasma-assisted chemical reactions have been widely used in the semiconductor and flat panel display industries. One example is plasma-enhanced chemical vapor deposition (PECVD), which is a process that is used in the manufacture of thin film transistors (TFT) for active-matrix liquid crystal displays (AMLCDs). In accordance with PECVD, a substrate is placed in a vacuum deposition chamber that is equipped with a pair of parallel plate electrodes. One of the electrodes, e.g. the lower electrode, generally referred to as a susceptor, holds the substrate. The other electrode, i.e., the upper electrode, functions as a gas inlet manifold or shower head. During deposition, a reactant gas flows into the chamber through the upper electrode and a radio frequency (RF) voltage is applied between the electrodes to produce a plasma within the reactant gas. The plasma causes the reactant gas to decompose and deposit a layer of material onto the surface of the substrate.
One material often deposited is silicon nitride (SiN). SiN is a common material for a gate insulation layer and also for passivation layers due to its ability to resist moisture and sodium contamination. In SiN deposition, as described in U.S. Pat. No. 5,399,387, assigned to the assignee of the present invention and herein incorporated by reference, a plasma of silane (SiH4) and ammonia (NH3) gases may be used to deposit SiN according to several reaction paths, for example:
xe2x80x83SiH4+NH3xe2x86x92SiNH+3H2
3SiH4+4NH3xe2x86x92Si3N4+12H2
SiN not only deposits on the substrate but also deposits on the walls and the pumping system. A known in-situ cleaning process may remove the SiN film from the walls by supplying a cleaning gas, often nitrogen fluoride (NF3), and activating the gas inside the chamber using an RF plasma in order to form pumpable volatile products. This reaction may proceed as follows:
NF3RF Plasmaxe2x86x92NFx+F
F+SiN RF Plasmaxe2x86x92SiF4+N2
The product silicon fluoride (SiF4) may then react with NH3 and hydrogen fluoride (HF) in the SiN deposition process to form, for example, ammonium silicon hexafluoride, (NH4)2SiF6. Such products and other silicon-containing fluoride products, are referred to herein as xe2x80x9cwhite powderxe2x80x9d, and more generally constitute partially reacted SiN films. This undesirable white powder can condense, for example, in the vacuum pump. The white powder can also condense in the vacuum line connecting the process chamber to the pump (the foreline) and in the vacuum line connecting the pump to the exhaust system (the exhaust line). Finally, the white powder can also condense in the burn box (which treats the exhaust) and on the chamber walls. In the case of the pump and exhaust, the condensation can amount to several kilograms of white powder, often causing pump failure. In the case of the foreline and the exhaust line, clogging can occur. The white powder is also a source of undesirable particulates in deposition processes.
Prior plasma in-situ cleaning processes are ineffective at removing the white powder or reducing its occurrence in SiN deposition. In such systems for cleaning the chamber and the exposed components within the chamber, precursor gases are supplied to the chamber. Then, by locally applying a glow discharge plasma to the precursor gases within the chamber, reactive species are generated. The reactive species clean the chamber surfaces by forming volatile compounds with the process deposit on those surfaces. This plasma in-situ cleaning generally does not remove the white powder, regular maintenance of the pump and exhaust is still required.
New enhanced cleaning systems are developed for removing the white powder. For example, some enhanced systems introduce an additional plasma source between the process chamber and the pump. In another example, traps are introduced between the pump and the process chamber or after the pump (in the exhaust line). However, these methods are also ineffective at removing the white powder or reducing its occurrence in SiN deposition.
It is an object of the present invention to reduce the amount of white powder formed during SiN deposition processes. It is a related object to reduce the damage to components that may occur as a result of white powder formation.
In one aspect, the invention is directed to a method for reducing the production of white powder in a process chamber used for depositing silicon nitride, comprising the steps of heating at least a portion of a wall of the process chamber; providing a liner covering a substantial portion of a wall of the process chamber; providing a remote chamber connected to the interior of the process chamber; causing a plasma of cleaning gas in the remote chamber; and flowing a portion of the plasma of cleaning gas into the process chamber, such that the production of white powder is substantially reduced.
Implementations of the invention include the following. The heating step is performed by flowing a heated fluid in at least one hollow compartment within the wall. The production of white powder is reduced in a vacuum line and a pumping system serving the process chamber. The heated fluid is substantially water. The method may further comprise the step of heating the water to a temperature of about 85xc2x0 C. or greater than about 85xc2x0 C. The liner covers substantially the entire interior portion of the process chamber. The liner is made of anodized aluminum or of a ceramic.
In another aspect, the invention is directed to a method for reducing the production of white powder in a process chamber used for depositing silicon nitride, comprising the steps of providing means for heating the walls of the process chamber and providing a liner covering a substantial portion of the interior of the process chamber, such that the production of white powder is substantially reduced.
Implementations of the invention include the following. The heating means is a thermally insulating blanket substantially covering the exterior of the process chamber or a resistive heater.
In another aspect, the invention is directed to an apparatus for silicon nitride deposition in which the production of white powder is reduced. The invention comprises a deposition chamber having walls; means for heating the walls, the means thermally coupled to the walls; a liner covering a substantial portion of the walls; a remote chamber disposed outside of the chamber; an activation source adapted to deliver energy into the remote chamber; a first conduit for flowing a precursor gas from a remote gas supply into the remote chamber where it is activated by the activation source to form a reactive species; and a second conduit for flowing the reactive species from the remote chamber into the deposition chamber.
Implementations of the invention include the following. The heating means includes a compartment located within at least a portion of the wall; a fluid inlet port connected to the compartment; and a fluid outlet port connected to the compartment. There is also a source of fluid connected to the fluid inlet port. The heating means may also be a thermally insulating blanket substantially covering the exterior of the chamber.
It is an advantage of the present invention that the amount of white powder produced in SiN deposition processes is reduced. It is a further advantage that the occurrences of pump failure and line clogging caused by white powder are reduced.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the claims.